1989 merc Alpha 1, gen 1 with GM V6 engine question

[Augoose]

My normal operating temp while under way is about 150-160 degrees. I noticed today that after running the absolute slowest idle speed I could while just screwing around and trying to troll for about 10 minutes, the engine temp increased to about 200. I sped up slightly, still at idle speed but just the faster end of idle speed and the engine temp soon settled down right back to about 150 degrees.

Is this normal? I have a new water pump and impeller in it. Do they not spin fast enough to pump enough cool water at extremely slow speeds possibly?

Thanks!

 

[Don S]

Re: 1989 merc Alpha 1, gen 1 with GM V6 engine question

No it's not normal, it should hold the same temp at all speeds. Sounds like you are due for a new impeller. They are only good for a couple of years, how old is yours?

 

[Augoose]

Re: 1989 merc Alpha 1, gen 1 with GM V6 engine question

No it's not normal, it should hold the same temp at all speeds. Sounds like you are due for a new impeller. They are only good for a couple of years, how old is yours?

Impeller is less than 4 months old according to the PO.

 

[bomar76]

Re: 1989 merc Alpha 1, gen 1 with GM V6 engine question

Replace the impeller.
Anything a prior owner (seller) tells you can be taken with a ton of salt.

Even if it was new 4 months ago you have no idea how long it may have been run dry, filled with sand, or even if it was done correctly.

 

[Augoose]

Re: 1989 merc Alpha 1, gen 1 with GM V6 engine question

Got it. Will order a new one tomorrow. Any concern about the water pump or is the fact that the engine is cooling at all suggest the pump is ok?

 

[cr2k]

Re: 1989 merc Alpha 1, gen 1 with GM V6 engine question

What you describe is common. But take a look at the base and housing. Looking for signs of melted plastic or the SS cup rotated in the housing. If found you need to replace them as well as they would be warped and not sealing correctly so even with new impeller you could still have cooling issues at idle do to water leaking around housing.

 

[Augoose]

Re: 1989 merc Alpha 1, gen 1 with GM V6 engine question

Thanks for the help all. I plan on tearing into it this weekend and I'll see what the issue is.

 

[liquidlew]

Re: 1989 merc Alpha 1, gen 1 with GM V6 engine question

If after you do all that and it still runs hot at idle, check your engine timing. Being off just a little might be the problem as it was for me once.

 

[Augoose]

Re: 1989 merc Alpha 1, gen 1 with GM V6 engine question

If after you do all that and it still runs hot at idle, check your engine timing. Being off just a little might be the problem as it was for me once.

Thanks for that suggestion as well. It only ran hot that one time and it was when I was barely making idle speed. In fact it was running normal (150 degrees) at idle and then I kept tapping the throttle to slow it down even more while trying to troll. That was when I noticed it go up to 200 degrees. I then sped up to a "normal" wake speed of around 5 kph I would guess, and the engine cooled right down again. I wouldn't say that it runs hot whenever I run at idle - rather it was just that one time.

Thanks again!